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From: Kees Cook <keescook@chromium.org>
To: Cong Wang <xiyou.wangcong@gmail.com>,
	Qitao Xu <qitao.xu@bytedance.com>,
	"David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org, Cong Wang <cong.wang@bytedance.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-hardening@vger.kernel.org
Subject: Re: [Patch net-next resend v2] net: use %px to print skb address in trace_netif_receive_skb
Date: Fri, 23 Jul 2021 00:09:15 -0700	[thread overview]
Message-ID: <202107230000.B52B102@keescook> (raw)
In-Reply-To: <20210715055923.43126-1-xiyou.wangcong@gmail.com>

On Wed, Jul 14, 2021 at 10:59:23PM -0700, Cong Wang wrote:
> From: Qitao Xu <qitao.xu@bytedance.com>
> 
> The print format of skb adress in tracepoint class net_dev_template
> is changed to %px from %p, because we want to use skb address
> as a quick way to identify a packet.

No; %p was already hashed to uniquely identify unique addresses. This
is needlessly exposing kernel addresses with no change in utility. See
[1] for full details on when %px is justified (almost never).

> Note, trace ring buffer is only accessible to privileged users,
> it is safe to use a real kernel address here.

That's not accurate either; there is a difference between uid 0 and
kernel mode privilege levels.

Please revert these:

	851f36e40962408309ad2665bf0056c19a97881c
	65875073eddd24d7b3968c1501ef29277398dc7b

And adjust this to replace %px with %p:

	70713dddf3d25a02d1952f8c5d2688c986d2f2fb

Thanks!

-Kees

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#p-format-specifier

> 
> Reviewed-by: Cong Wang <cong.wang@bytedance.com>
> Signed-off-by: Qitao Xu <qitao.xu@bytedance.com>
> ---
>  include/trace/events/net.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/trace/events/net.h b/include/trace/events/net.h
> index 2399073c3afc..78c448c6ab4c 100644
> --- a/include/trace/events/net.h
> +++ b/include/trace/events/net.h
> @@ -136,7 +136,7 @@ DECLARE_EVENT_CLASS(net_dev_template,
>  		__assign_str(name, skb->dev->name);
>  	),
>  
> -	TP_printk("dev=%s skbaddr=%p len=%u",
> +	TP_printk("dev=%s skbaddr=%px len=%u",
>  		__get_str(name), __entry->skbaddr, __entry->len)
>  )
>  
> -- 
> 2.27.0
> 

-- 
Kees Cook

  parent reply	other threads:[~2021-07-23  7:09 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-15  5:59 Cong Wang
2021-07-15 17:40 ` patchwork-bot+netdevbpf
2021-07-23  7:09 ` Kees Cook [this message]
2021-07-28  3:17   ` Cong Wang
2021-07-28 15:13   ` tracepoints and %p [was: Re: [Patch net-next resend v2] net: use %px to print skb address in trace_netif_receive_skb] Jann Horn
2021-07-28 15:56     ` Steven Rostedt
2021-07-28 18:48       ` Kees Cook
2021-07-28 18:56         ` Jann Horn
2021-07-28 20:41         ` Steven Rostedt

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